Attraction field

Question

What does the attraction field of TreeAttraction look like around a single tree and around a small forest? Where do their fields meet, and how does this depend on density_weight?

Setup

All parameters are set in run.jl.

  • Landscape: 1000 m × 400 m, 10 m cells. A single tree at x = 295 m, and a round, fully stocked forest with a radius of 60 m, centered at x = 695 m. Both are centered on the transect at y = 195 m.
  • Attraction: TreeAttraction for healthy trees, half_distance 50 m, density_radius 20 m. density_weight is varied: 0, 1 and 2.

For each density_weight, the field is calculated three times: for the single tree and the forest together, and for each of them alone. As the field is the maximum over all sources, the combined field is the maximum of the two separate ones, and the fields meet where these are equal.

Running

From the PWNModel.jl/ directory:

julia --project=explore explore/attraction_field/run.jl

Figures are written to out/ as SVG (and PNG). They are not committed, but shown on the web page.

Figures

Cross-sections

Attraction along the transect (log scale), for the tree and the forest together (black) and for each of them alone (dashed). The orange line marks where the fields meet. Green areas are trees.

Cross-sections

Maps

The attraction field (log₁₀, same coloring as the attraction view of the default config.yaml) with the trees (light green) and the transect (dashed). The orange line is where the fields of the tree and the forest meet.

Field maps

Observations

  • With density_weight 0, all trees seed the field with the same value, and the fields meet halfway between the tree and the forest edge.
  • With density_weight 1, the single tree's seed is lower than the forest's, by its local occupancy (1 of 25 cells). The forest's field takes over 70 m from the tree.
  • With density_weight 2, the forest's field is higher than the tree's even at the tree itself. Beetles following the field gradient pass the tree without stopping there.